Aromatic chalcogenazolium salts, such as benzoxazolium, naphthoxazolium, benzothiazolium, naphthothiazolium, benzoselenazolium, and naphthoselenazolium salts, as well as their azole, azoline, and azolinium derivatives, have been widely employed in silver halide photography. These compounds have been employed as nuclei in polymethine dyes, antifoggants or stabilizers, nucleating agents, latent image keeping addenda, and speed or contrast increasing addenda for silver halide photographic systems.
Although Schlichting U.S. Pat. No. 2,168,174 and Wilson U.S. Pat. Nos. 2,323,503 and '504 have extended generic ring formulae to include tellurazoles as extrapolations of investigations of other chalcogenazoles, the true state of the art is summed up by Middleton U.S. Pat. No. 2,339,094:
It may be observed that the difficulty of reaction resulting in the production of azoles containing members of the oxygen group of elements in the azole ring may vary greatly with different elements, becoming greater in proceeding from the non-metallic elements such as oxygen and sulfur to the more strongly metallic elements such as selenium and tellurium. This probably accounts for the fact that many of the oxazoles and thiazoles have been known for years while the preparation of most of the selenazoles has been accomplished more recently and some of them are still unknown although the corresponding oxazoles and thiazoles are known. Furthermore, the tellurazoles from the simplest to the more complex derivatives have not been described up to the present time.
While the art has heretofore been unsuccessful in preparing tellurazolium salts and their derivatives, it should be noted that divalent tellurium atoms have been placed in other ring structures. Benzisotellurazole-1,2 is described in "Un Nouvel Heterocycle Tellure: le Benzisotellurazole-1,2", by Campsteyn et al, Journal of Heterocyclic Chemistry, Vol. 15, August 1978, pp. 745-748. Unfortunately no derivative of benzisotellurazole-1,2 is disclosed. Without a 3 position substituent the ring structure is itself severely restricted as a possible photographic addendum. Further, in general isochalcogenazoles are less desirable and more infrequently suggested for use as photographic addendum than the corresponding chalcogenazoles, since the chalcogen to nitrogen bond in the ring is a potential source of instability.
Tellurium atoms have been incorporated in ring structures other than azole or azine rings of various dyes. Japanese Kokai No. 136420, laid open Nov. 25, 1976, discloses a 1-tellura-3,5-cyclohexanedione nucleus in a merocyanine sensitizing dye in a silver halide emulsion. Detty et al U.S. Pat. No. 4,329,284 discloses 1,2-oxachalcogenol-1-ium salts, wherein the chalcogen can be tellurium or selenium, to be useful in photoconductive compositions. Detty et al U.S. Pat. Nos. 4,365,016 and '017 disclose tellurapyrylium dyes for use in photoconductive compositions.